1. Field of the Invention
This invention relates to a fuel metering control system for an internal combustion engine
2. Description of the Related Art
It is known in the art to install an air/fuel ratio sensor at an exhaust confluence of a multicylinder internal combustion engine to detect the air/fuel ratio of engine exhaust, and to feedback control the air/fuel ratio to a desired value, as taught, for example, by Japanese Patent Publication No. Sho 62(1987)-20,365. In the prior art system, based on an output of a single air/fuel ratio sensor installed at the exhaust system, the confluence point air/fuel ratio feedback and the individual cylinder air/fuel ratio feedback are controlled at different times.
As disclosed in the reference, when feedback controllers operate using a single sensor as common inputs, there may sometimes occur interference between the controllers, rendering the control unstable. In particular, the problem is apt to occur more often when feedback controllers are provided in parallel or multi-imposed In addition, since the output of the air/fuel ratio sensor has noise, it is preferable to remove noise as much as possible so as to enhance detection accuracy.